Circuit arrangement for generating a saw-tooth current in a coil



Aprll 11, 1950 F. KERKHOF 2,503,745

CIRCUIT-ARRANGEMENT FOR GENERATING A SAW-TOOTH CURRENT IN A COIL Filed Dec. 26, 1947 5 ow toath V0 9 Gdhdrafcr Sawtooth V0 lt 98 Gaunt" INVENTOR. Faaosm K KERKHOF Patented Apr. 11, 1950 CIRCUIT ARRANGEMENT FOR GENERATING A SAW-TOOTH CURRENT IN A COIL Frederik Kerkhof, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 26, 1947, Serial No. 794,031 In the Netherlands January 14, 1947 6 Claims. 1

The invention relates to a circuit-arrangement for generating a saw-tooth current in a coil having a self-induction L and a resistance R, which current is derived from the voltage set up across an inductance coil at least part of which is included in the anode circuit of a discharge tube, whilst a diode is included in a circuit which is connected in parallel to at least part of this anode circuit in such manner that during the sweep of the saw-tooth current the diode is conductive.

It is the object of the invention to provide a circuit arrangement for generating a saw-tooth sweep current having a high degree of linearity.

A specific object of the invention is to provide an inductive type saw-tooth current generator of the above referred to type in which nonlinearities of the generated sweep current are corrected.

In accordance with the invention, these objects are achieved by including in the inductive circuit of the generator a further inductive element which varies in value proportional to the amplitude of the generated current.

The invention will be described in greater detail with reference to the appended drawing in which:

Figs. 1 and 2 are schematic diagrams of sawtooth current generators of the type to which the invention applies.

Fig. 3 is a schematic diagram of the equivalent circuit of the generator of Fig. 1,

Fig. 4 is a schematic diagram of a saw-tooth current generator according to the invention.

In the figures similar parts are denoted by the same numbers.

In the circuit-arrangement according to Fig. 1 the primary winding I of a transformer 2 has a portion thereof included in the anode circuit of a discharge tube 3 and the remainder thereof forms part of a circuit comprising a diode 4. Impulses are supplied to a control grid of tube 3 by means of a saw-tooth generator of conventional form.

A coil 6 which in practice constitutes the defiec tion coil of a cathode ray tube, is connected to the secondary winding of the transformer 2.

In the circuit-arrangement according to Fig. 2 the whole of the primary winding l of the transformer is included in the anode circuit of the tube 3. However, in this arrangement the anode of the diode 4, instead of being connected to the negative terminal of a battery I, is connected to a point of higher potential.

The operation of both circuit-arrangements is well-known but it is of importance to point out that with the circuit-arrangement according to Fig. 1 owing to the fact that only part of the primary winding I is included in the anode circuit of tube 3 and with the circuit-arrangement according to Fig. 2 owing to the fact that the anode of the diode 4 is connected to a tap on the battery l, the diode is conductive during the whole of the sweep of the saw-tooth current due to the induced voltage in the Winding l which makes the cathode of the diode more negative than the anode thereof. The consequence thereof is that with the circuit-arrangement according to Fig. 1 during the whole of the sweep the voltage across the total Winding i is limited by the diode to a value substantially equal to the voltage E of the battery '1, whereas with the circuit-arrangement according to Fig. 2, the voltage across the whole of the winding l is similarly limited to a value substantially equal to the voltage across the portion p of the battery I.

In the circuit-arrangement according to Fig. 1 the effect of the coil 6 may be referred to the primary side of the transformer 2, in which event during the sweep of the saw-tooth current the equivalent circuit according to Fig. 3 obtains, wherein L1 represents the transposed self-induction L of the coil 6 and r is the resistance of the diode increased by the transposed resistance R of the coil 6 and by the resistance of the winding I.

In this circuit we have:

If 1- is sufficiently small, its effect is negligible so that the current i varies linearly with the time 1.. If r is not sufilciently small, the current 2' varies exponentially with time.

The circuit-arrangement according to Fig. 4 obviates the above noted disadvantages and exhibits the feature that the coil 6 has connected in series with it a second coil 8, the self-induction of which decreases, upon increase of the intensity of the saw-tooth current traversing this coil, in such manner that during the sweep this current increases linearly or substantially linearly with time.

If the inductance coil 8 has a self-induction value (Lo being a constant value, 1- being the transformed resistance of the coil 6, which is required to be corrected, and

being constant), it has proved possible to obtain a sweep of the saw-tooth current which increases linearly with time.

In that case we have:

Due to the variable self -induction, a voltage -z'r, which exactly neutralizes the disturbing term '+ir, is set up across the coil 8.

As shown in Fig. '14, the coil comprising a core 9 which with the aid of the battery 7 is premagnetized via a variable resistance it and a choke coil l I in such manner that upon increase of the current flowing in the'circuit which includes the coil 6, the self-induction of the coil 8 decreases. To that end a premagnetisation may be brought about up to a 'value at which the sweep of the saw-tooth current takes place in that region of the magnetisation curve of the core material in which the self-induction varies linearly with the current intensity.

As the core material may be utilized, for example, a sintered magnetic ferrite. Even at small values of themagnetisationcurrent, the differential 'of the magnetisationcurve of this material has a substantially linear course. It has now been found to be possible to obtain the desired course by a suitable choice of the core material, adapted to the self-induction variation desired.

The choke coil it serves to prevent the impedance of the coil 3 from being'influenced by the premagnetisation circuit. Instead of the choke coil, use may alternatively-be made for this purpose of .a'discharge tube having a high internal resistance.

It may beobserved that for the purpose of premagnetizing the core it is not necessary to provide on that core a special winding, but that the direct-current circuit may include the winding of the 00118.

Itwill be evident that the correction coil 8 may alternatively be included in the primary circuit of the transformer 2, for example, between the primary winding 1 and the battery 7.

What I claim is:

1, An electrical circuit arrangement for generating a saw-tooth sweep current in a coil, comprising a discharge tube having a cathode, a control grid and an anode, means to apply a sawtooth voltage to said control grid, an inductance element interposed between said anode and cathode, means to couple said coil to said inductance element, a diode element shunting said inductance element. and being poled to be conductive during the current now through said inductance element and through said discharge tube, and a second inductance element connected in series with said coil, said second inductance element having an inductance which decreases in value with increases in the current therethrough.

2. An electrical'circuit arrangement for generating a saw-tooth sweep current'in a coil, comprising a discharge tube having acathodaa control grid and ananodaineans'to apply a sawtooth voltage to said control grid, an inductance element interposed between said anode and cathode, means to "couple said coil to said inductance'elem'enu'a diode element shunting said inductanceelement and being poled to be conductive during the current flow through said inductance element and through said discharge tube, and a second inductance element connected in series with said coil, saidsecondlinduotance element comprising a'corexof ferromagnetiomaterial and a magnetizing winding on said-core and having an inductance which decreases .in value with increases in the current therethrough.

3. An electrical circuitarrangement for generating a saw-tooth sweep current in a coil, comprising a dischargentube having a cathode, a control grid and an anode, means to apply a saw-tooth voltage to said control grid, an inductance element comprising a primary winding interposed between saidanode and cathode and to said secondary winding, a diode element shunting said primary winding and being poled to be conductive during the current flow through said primary winding-and through said discharge tube, and a second inductance element connected in series with saidcoil and said secondary winding, said second inductance element having an inductance which decreases in value with increases in the current therethrough.

4. An electrical circuit arrangement for generating a saw-tooth sweep current in a coil, comprising a discharge tube having a cathode, a control grid and an anode, means to apply a sawtooth voltage to said-control grid, an inductance element interposed between said anode and cathode, means to couple said coil to said inductance element, a diode-element shunting said inductance element and being poled to be conductive during the current flow through said inductance element :and through said discharge tube, and a second inductance element connected in series with said coil, said second inductance element comprising a core'of a sintered magnetic ferrite and a magnetizing winding on said core and having an inductance which decreases in value with increases in thecurrent therethrough.

5. An electrical circuit arrangement for generating a saw-tooth sweep current in a coil, comprising a discharge tube having a cathode, a control grid and an anode, means to apply a saw-tooth voltage to said control grid, an inductance element comprising a primary winding interposed between :said anode and cathode and a secondary winding, means to couple said coil to said secondary *winding, a diode element shunting said primary winding and being poled to be conductive during the current flow through said primary winding'and through said discharge tube, a second inductance element comprising a core of ferromagnetic material, a'first winding arranged on saidcore and connected in series with said coil and said secondary winding, and a second winding arranged onsaid core, and means to apply a direct current to said second winding to premagnetize said coreand impart to said first winding an inductance'which decreases in value with increases in the current therethrough.

6. An electrical circuit arrangement for generating a saw-tooth sweep current ina coil, comprising a discharge tube having a cathode, a control grid and an anode, means to apply a sawtooth voltage :to said control grid, an inductance element comprisinga primary winding havinga tapping, and a-secondary winding, means to connect said tapping to saidanode, means to couple said coil to said secondary winding, a diode elementshunting said primary winding and being poled to be conductive during the current flow through said primary winding and through said discharge tube, and-a second inductance element comprising a core of ferromagnetic material, a first winding arrangedon said core and connected in series with said coil and said secondary vwinding, and a second winding arranged on said core, a source of a direct current connected to said second winding to premagnetize said core and impart to said first winding an inductance which decreases in value with increases in the current therethroughand a choke coil interposed between saidsecond windingand said source.

FREDERIK KERKHOF.

No referencescited. 

